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Light travels at a speed which is about

题库2022-08-02  57
问题 Light travels at a speed which is about a million times faster than the speed of sound. In one second, light travels about 300,000 km. But sound travels only 344m. You can get some idea of his difference by watching the start of a race. If you stand some distance away from the starter, you can see smoke comes from his gun before the sound reaches your ears.　　This great speed of light gives us some strange facts. Sunlight takes about 8 minutes to reach us. If you look at the light of the moon tonight, remember that the light left the moon 1.3 seconds before it reached you. The nearest star is so far away that the light which you can see from it tonight started to travel towards you four years ago at a speed of nearly 2 million km per minute. In some case, the light from one of tonight's stars started on its journey to you before you were born.　　Thus, if you want to be honest, you can say "The stars are shining to night?" You have to say“The stars look pretty. They were shining four years ago but their light has just reached Earth. "We can know from the information given in the passage that the moon must be about ____ away from us.（　　）A. one million km B. 350,000 km C. 300,000 km D. 400,000 km
选项 A. one million km
B. 350,000 km
C. 300,000 km
D. 400,000 km
答案 D
解析 从文章“light travels about 300,000km”和“the light left the moon 1.3 seconds before it reached you.”中可知，根据计算300,000×1.3≈400，000。
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